Slate is a metamorphic rock with a dull luster. The most common color of slate is gray, but it can also be brown, green, purple, or blue. Slate is formed when a sedimentary rock (shale, mudstone, or basalt) is compressed. Over time, slate may transition into other metamorphic rocks, such as phyllite or schist. You’ve likely encountered slate on a building or an old … Continue reading What is Slate?